Method of making a photographic sensitive element



tions.

Patented Sept. 23, 1952 METHOD OF MAKING A PH O'TOGRAPHIC' SENSITIVE ELEMENT. V

Willem Robijns, Antwerp-Mortsel, Belgium, as-

signor to Gevaert Photo-Producten .N'. V.,

Mortsel-Antwerp, Belgiu gium m, a company of Bel I No Drawing. Application March 18, 1947, Serial No. 735,528. In Belgium June28, 1946 1 Claim. (01.117-34) The invention relates to'a photographic material, especially photographic paper, and to a method of manufacturing same.

The primary object of the present invention is I to generally improve photographic materials used toobta'in images with pastel-like appearance.

in order to obtain pastel-like photographic images, that is to say, images having an absolute mat surface and a high maximum black value, it is known to use a photographic material using a support, for instance, paper, coated with an adhesive material having sensitized dust fibers uniformly distributed thereon. These fibers are made light-sensitive either before or after they are applied to the support, no binder being used for the light-sensitive salts. Different lightsensitive substances are in common use; these include silver halide, chromic and ferric salts, diazo compounds.

In the known processes for making photographic materials for images with pastel-like appearance, the silver halide is formed directly on the fibers of the velvety support by spraying aqueous solutions of silver nitrate and alkali halide thereupon. The prior processes in which the photographic emulsion, such as a silver halide emulsion, is not obtained in the usual manner whereby the silver halide is formed in the presence of a protecting colloid, have been found unsatisfactory to secure optimum condi- The silver halide being precipitated directly on the fibers of the base, the solutions of the silver salt and alkali halide cannot be used in the most favorable proportions. An important object of my invention is to provide a method of making photographic materials for images with pastel-like appearance whereby the emulsion is prepared before it is applied to the base. A more specific object is to prepare the emulsion in the presence of a protecting colloid.

It is another object of the present invention to provide a method whereby an emulsion is employed which has been prepared using the usual distinct steps, such as ripening, washing, stabi lizing, etc.

It is known that the photographic material prepared according to the prior processes does not possess the desired properties, such as regularity, stability and high sensitivity. The invention aims, therefore, at a photographic material which will not have the disadvantages of the prior art materials, but instead will embody more specific objects which will hereinafter ap- 2 I v pear, my invention resides in the photographic material and method of -making the same, as are more particularly described hereinafter.

-I havediscovered that a-satisfactoryiphotographic material of'thekind contemplated can be obtained by using a photographic emulsion having the characteristics disclosed below in combination with knownvelvety supports. In producing the emulsion, it is one feature of my inventionv that theemulsion is formed in a solu f tion of gelatine or another protecting colloid.

According to another feature of my present invention, the emulsion is completely prepared before it is applied to the velvety support. The emulsion may be ripened, washed, digested, provided with the usual addition substances, and is finally coated upon a velvety support in the same way as other photographic emulsions.

In accordance with this invention, I use an emulsion which in relation to the binder possesses a high content of silver. Where gelatine silver halides are employed, the ratio of silver nitrate to gelatine must be at least 1.5 to 1. This ratio is also applicable to other light-sensitive substances.

Furthermore, the emulsion of the invention has a very low viscosity. With the above indicated ratio, the viscosity of the finished emulsion shall not exceed the viscosity of a four percent aqueous solution of usual photographic gelatine.

It has been found that in coating emulsions having the two above described characteristics on a velvety support, each fibre will be completely surrounded by a thin coating of the light-sensitive layer. It has also been found that this lightsensitive colloid penetrates into the depth of the cavities formed by the loose fibres, thus giving the image an optimum appearance of depth.

In an illustrative but non-limiting example of the method of my invention, the following solutions are prepared:

Solution A Potassium bromide J g 200 Distilled water cm. 300

Solution B Silver nitrate g 250 Distilled water cm. 500 Ammonia D 0.91 cm.= 200 Solution C I Distilled water cm. 1500 Gelatine g The Solutions A and B are added to Solution 0 within 20 seconds at a temperature of 15 C. The

mixture is ripened until the desired sensitiveness is obtained, permitted to solidify, and washed. The emulsion is now melted at 40 C. and ripened at this temperature for one hour. Before coating, 30 cm. of a2.5 per cent solution of saponine and 50 cm. of a per cent solution of chrome alum are added. Finally, water is added until the emulsion contains 3 per cent gelatine.

While I have described hereinbefore certain embodiments which my invention may assume, it

will be understood that these embodiments are merely for the purpose of illustration and that other forms may be devised. For-'in'stance, instead of silver, any other light-sensitive substance, and instead of gelatine, any other colloid may be used.

It is clear that my new process forthe prepa- I ration of velvetlike photographic paper is independent of the sensitiveness or the gradation of the emulsions so that the scope of my invention involves any combination of a velvetlike paper support with a photographic emulsion whenever the latter is characterized'by a high proportion of light-sensitive substances in respect to the binder and by a very low viscosity within the limits of the appended claim.

Method of manufacturing photographic material for obtaining photographic images with pastel-like appearance, which comprises app y- Number WILLEM ROBIJ NS.

REFERENCES CITED The followingreferences are of record in the file of this patent:

UNITED STATES PATENTS Name Date 1,593,652 Donauer July 27, 1926 1,752,665 Friedlander Apr. 1, 1930 2,006,002 Schneider June 25, 1935 2,192,241 Robijns Mar. 5, 1940 2,384,857 Terry Sept. 18, 1945 FOREIGN PATENTS Number I Country Date 17,303 Great Britain of 1905 274,075 Great Britain Jan. 26, 1928 486,252 Great Britain June 1, 1938 531,243 Great Britain Jan. 1, 1941 555,785 Great Britain Sept. 8, 1943 

